Submitted to: American Chemical Society Symposium Series
Publication Type: Book / Chapter
Publication Acceptance Date: July 30, 1999
Publication Date: N/A
Technical Abstract: In the Loess Hills along the Missouri River valley of southwestern Iowa, field studies are underway to determine the impact of continuous corn production on both surface water and groundwater quality. The landscape is characterized by gently sloping ridges, steep side slopes, and well-defined alluvial valleys often with incised channels that usually terminate at an active gully head. Surface water quality is evaluated by analyzing field runoff for nitrate-N, atrazine and metolachlor. A comparison among four watersheds under different tillage practices reveals different responses to an early spring event. In each case, the long-term impact resulting from more than 20 years of nitrogen fertilization and more than 15 years of atrazine and metolachlor application is assessed. Beneath the snow cover of March 1993, a diurnal freeze-thaw cycle was observed to cause displacement of both nitrate-N and parent herbicides (from past and current application) in surface runoff generated by melting snowcover. During the five days of repetitive events, the nitrate-N and herbicides exhibited different displacement patterns, perhaps as a result of their fundamentally different chemical properties.